RoK brings back the Quest in EQ2, providing a wealth of content for soloing while also raising the overall challenge.
RoK has four major overland zones. Continuing with the precedent set by the Echoes of Faydwer (EoF) expansion, the majority of content in these zones is soloable. That does NOT mean easy in this expansion, however. The base damage done by mobs auto attack and abilities has been raised significantly and the possibility of double attack has been added. This has resulted in a MUCH higher level of difficulty for soloing than anything since the first expansion, Desert of Flames. Unless their spells/Combat arts are fully upgraded and they are decked out in the highest caliber gear from raiding in EoF, players should expect to die occasionally and frequently if they are not careful and competent. While at first this threw me off, as it makes some of the questing and exploration much slower than I was accustomed to, I found myself enjoying this new level of challenge, since it brought a sense of achievement back to completing quest lines.
Not only was there a higher sense of achievement, but the rewards for quest lines in the expansion are vastly greater than any other quests in the game. Not only were the stats appropriately raised, but many powerful effects such as % to spell/melee crit and +spell/combat art damage were added. This level of reward made it worthwhile for even many raid geared players to go do the quests in the expansion. This also removed some of the pressure to gear up by repeatedly running the same instances endlessly.
Sticking with the model of higher challenge, instances in the expansion are much more difficult than previous group content. While the challenge is nice, two of the five new instances have encounters so difficult that it requires certain classes to be in your group to complete them. This is possibly the only negative aspect of the expansion, as it forces many players who are not in guilds with certain classes to have to look elsewhere to find the players necessary to finish an instance. Friends who may have normally grouped together will be unable to finish these two instances if they do not posses the required classes. However, I suspect that this limitation may be overcome as players become geared out in high quality legendary or higher gear later in the expansion life. That being said, the expansion has gone a long way to add strategy back into instances. Many named fights require learning how to approach them instead of just tanking and nuking them down.
The art design in the expansion has also gone up a step. The zones are all designed around the idea of having a center of focus as you progress through a zone. For example, you start out in one zone and the first thing that catches your eye as you move forward is a enormous bridge crossing a chasm with a small town on top of it. Moving past that draws your attention to a large mountain in the distance. Beyond that is a great field with the skeleton of a gigantic dragon. You don't see the next bit of eye candy until you travel past the current area. Of course, the natural quest progression in these zones matches the way your eye is drawn from point to point.
Both music and normal UI functions also received an upgrade. Combat music is now designed to reflect the current situation during a fight. As you get closer to death the music takes on a more frantic and dangerous nature. UI improvements came in the form of an upgraded persona window which tracks many of the melee and spell bonuses a character can have, as well as a revamp on the crafting window.
Overall, while this expansion does have a few drawbacks, I'd say it was a great step forward for the game as a whole. The level of detail and depth of play continue to keep Everquest 2 as the most immersive MMO on the market.